• Resources Recycling
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• v.29 no.6
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• pp.104-113
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• 2020

Bubble size in froth flotation has long been recognized as a key factor which affects the bubble residence time, the bubble surface area flux (Sb) and the carrying rate (Cr). This paper presents method of bubble size measurement, relationship between operating variables and gas dispersion properties in flotation column. Using high speed camera and image analysis system, bubble size has been directly measured as a function of operating parameters (e.g., superficial gas rate (Jg), superficial wash water rate (Jw), frother concentration) in flotation column. Relationship compared to measured and estimated bubble size was obtained within error ranges of ±15~20% and mean bubble size was 0.718mm. From this system the empirical relationship to control the bubble size and distribution has been developed under operating conditions such as Jg of 0.65~1.3cm/s, Jw of 0.13~0.52cm/s and frother concentration of 60~200ppm. Surface tension and bubble size decreased as frother concentration increased. It seemed that critical coalescence concentration (CCC) of bubbles was 200ppm so that surface tension was the lowest (49.24mN/m) at frother concentration of 200ppm. Bubble size tend to increase when superficial gas rate (Jg) decreases and superficial wash water rate Jw and frother concentration increase. Gas holdup is proportional to superficial gas rate as well as frother concentration and superficial wash water rate (at the fixed superficial gas rate).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.11-18
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• 2021

Nano bubble water is used in various washing processes, including cleaning of solar panels, salt rejection of roads, and cleaning precision parts of machines. High cleaning efficiency and water conservation are obtained by applying nano bubbles during pretreatment of the marine waste cleaning system. This study compared the salt rejection of nano bubble water, and it was revealed that marine waste was produced by wood immersed in 200,000 mg/L NaCl solution. Using tap water and nano bubble water for washing, comparisons of the surface salt concentrations of wood were determined according to the nozzle, orifice diameter, pump speed and washing time. Decreased surface salt concentration was observed on the wood surface with increasing washing time. Water consumption was optimal between 5- and 10-seconds washing time. Increasing orifice diameter of the nozzle reduced the spraying pressure, with consequent increase in the wood surface salt concentration, thereby establishing the importance of orifice diameter of the nozzle. Compared to levels obtained with tap water, salt concentration of the wood surface after washing with nano bubble water was 2.2% lower with sector nozzle, and 30.9% lower with circular nozzle. In the washing experiment using nano bubble water, the salt concentration on the wood surface was about 9.5 mg/L lower when washed with sector nozzle than the circular nozzle.

• Journal of the Korean GEO-environmental Society
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• v.12 no.4
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• pp.5-15
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• 2011

This study is conducted to find out the effect of vibration on cure and compressive strength of lightweight Air Trapped Soil(ATS). If ATS is used next to a structure existed, the effect of vibration problems may be occurred, because there exist many sources of vibration such as pile driving, blasting and use of construction machinery. For example, if a road is expanded to reduce traffic congestion, it is expected that ATS's quality may be decreased due to vibration generated by cars moving on the road. Especially, because ATS has many air bubbles and needs a time for curing, the effect of vibration is more serious than we expected. So far, the effect of vibration on concrete has been conducted, but the study of ATS has not been conducted in detail. Therefore, for evaluating the effect of vibration on ATS during cure proceeds, unconfined compression tests are conducted on the samples prepared with different variables including vibration velocity, time when vibrated and mixing ratio. The results clearly show the effect of vibration on the characteristics of ATS.

• International Area Studies Review
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• v.20 no.1
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• pp.105-125
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• 2016

The expansionary monetary policy was practiced after 2001 in Japan to treat the deflation spiral, and reduced only the nominal interest rates and domestic household demand. One of the most serious factors for this failure was the change of private sector's expectancy. This paper has studied the effect of Japanese monetary policy in 21c., with empirical research based on a renewed macroeconomic model and the VAR. The empirical analysis shows that the effect of monetary policy on the national income during 2001.01-2015.03 is weaker than that of 1985.01-1994.04. Money volume has a diminutive effect on the growth of GDP within a short term after 2001. The change in the expectations of the private sectors might have been the cause of ineffectiveness of the expansive monetary policy. Economic agents learned from the past Japanese financial crisis that an expansive monetary policy increased the inflation rate and caused the 'bubbles to burst' afterwards. The VAR analysis says that the effectiveness of monetary policy on the economic depression declined over the past 20 years and the expansion of money volume has no influence on exchange rate and net export. This means that the expansive monetary policy lost its effect on net export and national income steadily. Monetary policy makers have to recognize this fact, and to consider another anti-cycle political instrument, i.e. the fiscal policy with government debt.

• Journal of the Korea Convergence Society
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• v.12 no.3
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• pp.197-204
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• 2021

This study relates to a device that increases efficiency by reducing air bubbles in a hydraulic system used in hydraulic machinery. The reverse design and product production of the bubble reduction device, which is a commercial product overseas, was carried out. Overseas commercial products were set as the base model, a rotary rotor and an inclined rotor were added to increase the surface area of the fluid, and an annular equal distribution part with a slot in the lower part was additionally applied to distribute the fluid evenly. In addition, internal flow trends were analyzed and a system that evenly distributes the linear flow of fluid was selected as the first improvement model. Based on the first improvement model, a case where the angle of the inclined rotor is 45° was selected as the second improvement model. Based on this, as a result of setting the exit width of the annular equally distributed part as a variable, the bubble reduction efficiency was highest when the lower slot diameter of the annular part was 10mm. Finally, the system in which the average cross-sectional flow velocity decreased by 147% compared to the Base Model was derived as the final improved model.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.6
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• pp.442-454
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• 2021

The porous transport layer (PTL) is essential to effectively remove oxygen and hydrogen gas from the electrode surface at high current density operation conditions. In this study, the effect of PTL with different characteristics such as pore size, pore gradient, interfacial coating was investigated by multi-layered sintered mesh. A water electrolysis single cell of active area of the 34.56 cm² was constructed, and IV performance and impedance analysis were conducted in the range of 0 to 2.0 A/cm². It was confirmed that the multi-layered sintered mesh PTL, which have an average pore size of 25 to 57 ㎛ and a larger pore gradient, removed bubbles effectively and thus seemed to improve IV performance. Also, it was confirmed that the catalytic metals such as Ni, NiMo coating on the PTL reduced activation overpotential, but increased mass transport overpotential.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.61-68
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• 2021

Experiments of vertically upward steam-water two-phase flow have been carried out in single-side heated narrow rectangular channel with a gap of 3 mm. Flow patterns were identified and classified through visualization directly. Slug flow was only observed at 0.2 MPa but replaced by block-bubble flow at 1.0 MPa. Flow pattern maps at the pressure of 0.2 MPa and 1.0 MPa were plotted and the difference was analyzed. The experimental data has been compared with other flow pattern maps and transition criteria. The results show reasonable agreement with Hosler's, while a wide discrepancy is observed when compared with air-water two-phase experimental data. Current criteria developed based on air-water experiments poorly predict bubble-slug flow transition due to the different formation and growth of bubbles. This work is significant for researches on heat transfer, bubble dynamics and flow instability.

• Journal of Space Technology and Applications
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• v.2 no.2
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• pp.104-120
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• 2022

The Small Scale magNetospheric and Ionospheric Plasma Experiment (SNIPE)'s scientific goal is to observe spatial and temporal variations of the micro-scale plasma structures on the topside ionosphere. The four 6U CubeSats (~10 kg) will be launched into a polar orbit at ~500 km. The distances of each satellite will be controlled from 10 km to more than ~1,000 km by the formation flying algorithm. The SNIPE mission is equipped with identical scientific instruments, Solid-State Telescopes(SST), Magnetometers(Mag), and Langmuir Probes(LP). All the payloads have a high temporal resolution (sampling rates of about 10 Hz). Iridium communication modules provide an opportunity to upload emergency commands to change operational modes when geomagnetic storms occur. SNIPE's observations of the dimensions, occurrence rates, amplitudes, and spatiotemporal evolution of polar cap patches, field-aligned currents (FAC), radiation belt microbursts, and equatorial and mid-latitude plasma blobs and bubbles will determine their significance to the solar wind-magnetosphere-ionosphere interaction and quantify their impact on space weather. The formation flying CubeSat constellation, the SNIPE mission, will be launched by Soyuz-2 at Baikonur Cosmodrome in 2023.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.4
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• pp.128-135
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• 2022

The inside of a quartz glass crucible for semiconductor processing, called a transparent layer, is manufactured using synthetic silica powder. Bubbles existing in the transparent layer of the crucible cause a problem of reducing the quality of the crucible as well as the yield of the silicon ingot. Therefore, the main goal of the synthetic silica powder, which is the raw material of the transparent layer, is to minimize the bubble generation factor. For this purpose, in the case of synthetic silica powder, it is necessary to minimize silanol groups, carbon and pores. In this study, synthetic silica gel was prepared using the sol-gel method, and changes in carbon content and specific surface area were investigated according to calcination temperature and dwelled time in a two-stage calcination process. The first-stage calcination process was performed between 500℃ and 600℃ and the second-stage calcination process was performed between 1000℃ and 1100℃. The dwelled time was carried out from 10 minutes to a maximum of 12 hours. The carbon content of the powder calcined at 1000℃ for 1 hour was 0.0031 wt.%, and the specific surface area of the powder calcined at 1100℃ for 12 hours was 16.6 m²/g.

• Korean Journal of Veterinary Service
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• v.45 no.4
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• pp.325-330
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• 2022

Distichiasis is one of the diseases commonly encountered in companion animals, and these abnormal eyelashes cause corneal ulcers, continuous eye irritation, eye pain, glare, epiphora, foreign body sensation and can cause corneal opacity and vision loss in severe cases. In this study, an eyelash epilation needle for animals was developed and applied to a real case, and the results were observed. In a case of corneal ulcer caused by distichiasis of a 2-year-old Shih Tzu, a high-frequency surgical instrument for animals was converted into an electric epilation needle to attempt a procedure to destroy the eyelash hair follicles on the upper eyelid. A epilation needle was developed to have a diameter of 0.1 mm and a length of 4 mm at the end of the handle of DOCTANZ 400, an electrosurgical instrument for animals only. In the procedure, 2~3 mm of an epilation needle was inserted into the hair follicle, and 1 watt of electric power was applied to the hair follicle for about 5 sec. to carry out electrolysis until white bubbles were generated around the meibomian glands thereby destroying the hair follicle. As a result, no eyelashes grew any longer in the treated area indicating that the treatment was successful. It is hoped that the method developed in this study will be applied so that it will be widely used as a treatment method for distichiasis in companion animals that can be frequently seen hereafter.